On 2015-04-29 at 21:20, [email protected] <[email protected]> wrote: >On Tue, Apr 28, 2015 at 10:37 PM, [email protected] ><[email protected]> wrote: >> Hi, >> >> The encoder allows you to set the MaxQp(0~51), MinQp(0~51), and MaxBitrate >> >> parameters. MaxQp and MinQp are used to controlpicture quality and >> MaxBitrate >> >> is used to clamp the maximum encoding bit rate within the bitrate >> statistical >> >> time; >> >> The default configuration is MinQp = 10; MaxQp = 40. If you could not get >> >> it to work for lower bitrates , please try to change MaxQp to a bigger >> value, > >The bitrate setting on an h.264 encoder is supposed to take precedence >and be a hard limit. So if I set 500Kb/sec the encoder has to adjust >everything else until it can hit and hold that limit. Min/MaxQp should >not overrule the Bitrate limit. I believe the only exception to that >is for VBR where you are allowed to exceed the bandwidth limit by 10% >for short periods of time. The encoder is also supposed to be smart on >how it adjusts itself when the bandwidth limit is set. > >These limits are there for streaming video. I needed to set a 500Kb/s >hard limit because I only had 500Kb/s of streaming capacity available. >I couldn't figure out how to keep the Allwinner encoder at a 500Kb/s >limit, it would stay at 500Kb/s for a while but then if there was >rapid motion it would jump to 2Mb/s. It should not matter if CBR or >VBR is set, the limit should still be enforced. Of course when it >jumped to 2Mb/s on my 500Kb/s pipe, the stream dropped. > Nowadays, the limits of streaming video can't be controlled accurately with every frame, but an average in a period. On the A20 platform, it can't reach 500kb/s with 720p@30fps, the lowest value should be 1.5Mb/s.
>Check out the the software x86 h.264 implementations - they will >output exactly 500Kb/s when told to. You can watch the picture become >very clear when the scene is still and then go grainy when there is >rapid motion. > >Also - I had severe problems with noise on A20 cameras. That noise is >random from frame to frame. Encoding that noise wastes all of my >500Kb/s bandwidth which makes the image quality terrible. Typical >some type of ISP is used to remove this noise before h.264 encoding. > There may be 3 main factors causing noise, they are lens, Sensor and ISP. A20 has none local ISP, selecting an external ISP may reduce the noise. Besides ISP, the lens and Sensor is important too, and the NT99141 is recommended. >Does the Allwinner V3 support external I2S? I'd just look in the >datasheet, but it is too much hassle to get it. Yes, V3 can support external IIS. We will make the documents for v3 ready as soon as possible. ---------------- Best Regards, kevin.z.m -- You received this message because you are subscribed to the Google Groups "linux-sunxi" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
